USE master 
GO
CREATE DATABASE TestTxMark1
GO

USE TestTxMark1
GO
CREATE TABLE TestTable1
(
    ID INT,
    VALUE UNIQUEIDENTIFIER
)

-- insert some data into the table so we can have a starting point

INSERT INTO TestTable1
SELECT  ROW_NUMBER() OVER(ORDER BY number) AS RN, NULL
FROM    master..spt_values
ORDER BY RN

SELECT  *
FROM    TestTable1
GO

-- TAKE A FULL BACKUP of the databse
BACKUP DATABASE TestTxMark1 TO DISK = 'c:\TestTxMark1.bak'
GO

-- start a marked transaction that modifies both databases
BEGIN TRAN TxDb WITH MARK
    -- update values from NULL to random value
    UPDATE TestTable1
    SET VALUE = NEWID();
    -- update first 100 values from random value 

    -- to NULL in different DB
    UPDATE TestTxMark2.dbo.TestTable2
    SET VALUE = NULL
    WHERE ID <= 100;
COMMIT
GO

-- some time goes by here 
-- with various database activity...

-- We see two entries for marks in each database. 
-- This is just informational and has no bearing on the restore itself.
SELECT * FROM msdb..logmarkhistory

USE master
GO
-- create a log backup to restore to mark point
BACKUP LOG TestTxMark2 TO DISK = 'c:\TestTxMark2.trn'
GO
-- drop the database so we can restore it back
DROP DATABASE TestTxMark2
GO

-- RESTORE THE DATABASE BACK BEFORE OUR TRANSACTION
-- restore the full backup 
RESTORE DATABASE TestTxMark1
    FROM DISK = 'c:\TestTxMark1.bak'   
    WITH NORECOVERY;

-- restore the log backup to the transaction mark
RESTORE LOG TestTxMark1 FROM DISK = 'c:\TestTxMark1.trn'
    WITH RECOVERY, 
         -- recover to state before the transaction
         STOPBEFOREMARK  = 'TxDb';
         -- recover to state after the transaction
         -- STOPATMARK = 'TxDb';
GO

-- RESTORE THE DATABASE BACK BEFORE OUR TRANSACTION
-- restore the full backup 
RESTORE DATABASE TestTxMark2
    FROM DISK = 'c:\TestTxMark2.bak'
    WITH NORECOVERY;

-- restore the log backup to the transaction mark
RESTORE LOG TestTxMark2 FROM DISK = 'c:\TestTxMark2.trn'
    WITH RECOVERY, 
         -- recover to state before the transaction
         STOPBEFOREMARK  = 'TxDb';
         -- recover to state after the transaction
         -- STOPATMARK = 'TxDb';
GO

USE TestTxMark1
-- we restored to time before the transaction 
-- so we have NULL values in our table
SELECT * FROM TestTable1

USE TestTxMark2
-- we restored to time before the transaction 
-- so we DON'T have NULL values in our table
SELECT * FROM TestTable2